1. Field of the Invention
The present invention relates to a multipurpose detector for detecting a number of different types of event.
2. Description of the Related Art
It is known that passive infrared detectors can be used for detecting flames by detecting emissions from hot carbon dioxide using a narrow bandpass filter centered on a wavelength of 4.3 xcexcm. By using an array of detector elements, spatial information can be obtained which permits additional information, such as the size and location of the flames, to be deduced.
Furthermore, by analyzing signals from different parts of the spectrum, the performance of a flame detector can be enhanced. Typically, this is implemented by using up to three discrete detectors, each with a filter sensitive to an appropriate part of the spectrum.
It is also known that when fitted with a 5.5 xcexcm long wave pass filter a passive infrared detector can be used to detect people. By using an array of detector elements, as in the case of the flame detector described above, spatial information can be obtained which permits additional information such as the number and location of people in the field of view, to be obtained. In addition, the detection of people can be used in a range of specific applications, e.g. door opener, intruder detector or activity monitor, by using different algorithms to implement the particular detection requirements in each case.
There has been long-term interest in detectors capable of detecting both fires and people, but the optical requirements of each of the conventional detector types have made this impractical, such that different detectors are typically used in each case.
The present invention provides a multipurpose detector comprising:
an array of passive infrared detector elements;
optical collection means for focusing broadband radiation from a scene onto the array;
means for processing signals from the detector elements; and
filtering means providing a filter configuration allowing only a narrower range of radiation within a broadband to reach the detector elements and having means for moving the filter configuration to or from an operative position between the array and the scene, wherein the means for moving the filter configuration is operated in response to a control signal from the means for processing signals.
Preferably, the filtering means provide two or more filter configurations selectable to allow different ranges of radiation to reach the detector elements. In a preferred embodiment, the selection of different ranges of wavelengths allows performance benefits to be obtained by examining different parts of the spectrum, without the need to use multiple arrays, with the inherent cost penalty and difficulties of alignment. By processing the signals from the array appropriately, it is possible to use selectable spectral information in conjunction with the spatial information from the array to provide additional functionality compared with a conventional array-based detector. For example, the combination of spatial and spectral information may be used to detect fires that are not generating flames.
In addition, in a preferred embodiment, a single detector may be used to detect entirely different events such as the presence of people and fires, by selecting different filter configurations together with appropriate signal processing and detection algorithms in each case. Such a device may be selected to operate either as a fire detector or a people detector at a particular time, or otherwise may be operable to continuously scan for both fires and people. In a further embodiment, the spatial information may be used to distinguish between allowable and unallowable events, such as the presence of fires and/or people, in particular areas of the scene.
The detector array itself typically comprises a planar or substantially planar array of individual passive infrared detector elements, which may be pyroelectric detector elements. The broadband radiation permitted to pass onto the array by the optical collection means typically comprises at least the range of wavelengths capable of being detected by the detector elements being used. For passive infrared detectors, this broadband radiation is generally within the wavelength range of 2 xcexcm to 20 xcexcm.
In a particularly preferred embodiment, the filter configuration is selectable in response to a control signal generated by the signal processing means. This signal may effect implementation of the available filter configurations sequentially, or may alternatively cause the selection of a particular filter configuration which may enable more information to be determined about an event occurring in the scene or enable confirmation of the type of such an event.